Not an (exact) spec, but laying out a few notes to help:
Count this by the # of yearling badges awarded, that allows someone to take a break without resetting the counter completely. Doesn't have to be consecutive years.
'Decadian' isn't a word (there's no formal salutation I can find for something that turns 10), but I think we need to make this a gold badge that describes something that gets better with age. Cheese comes to mind, but some folks don't care for animal products in their bling, wine has alcohol, as does fruitcake. Hmmm....
'Decadated' is a play on dedicated, but not sure if that's too cheesy (or cheesy enough (see previous point))
There's also something we could conceivably open up to someone that has ten years of active experience on the site (while a padded room is appropriate, this would need to be delivered digitally), or maybe we could send someone an award for this. We're open to suggestions.
Anyway, we've got less than 6-8 weeks before folks start collecting double-digit yearling badges, so we need to come up with specifics pretty quickly :)